fix run-time issue

installHook.js:1 TypeError: Cannot read properties of undefined (reading '0')
    at index-rjtklWbg.js:488:22731
    at Array.map (<anonymous>)

src/features/theme/themeSlice.ts

@@ -1,7 +1,7 @@
 import { createSlice } from "@reduxjs/toolkit";
 import { RootState } from "redux/store";
 
-interface ThemeState {
+export interface ThemeState {
   themeName: string;
 }